A. Field of the Invention
This invention relates to porous, e.g. fibrous, articles structurally strengthened by inorganic resin impregnant compositions and to processes for forming them and articles of manufacture including such solid, porous articles, such as paper, fibrous webs of cellulose, glass or synthetic fibers impregnated with the inorganic resin composition and, more particularly, to inorganic resin cement articles having a unique combination of properties and a wide range of uses. A water composition containing a source of magnesium oxide and/or wollastonite is impregnated into the porous substrate to provide a reactive substrate capable of long storage life. The reactive substrate then is impregnated with a magnesium phosphate or aluminum phosphate composition causing a reaction with the magnesium oxide to form a resin bound article of manufacture. The inorganic resin cements are formed in situ within an initially porous article in accordance with the principles of the present invention and may be formed as noncellular or cellular structures.
B. Prior Art
A number of inorganic resin cement systems are known. Some are formed of magnesium oxychlorides or magnesium oxysulfates (U.S. Pat. Nos. 3,320,077; 4,141,744; and 4,315,967); and others are formed using phosphates and magnesia. Exemplary of this latter type are compositions of an acid magnesium phosphate, magnesia, silica, mineral fibers and water in an amount from 70 to 140% of the weight of the remaining components (U.S. Pat. No. 3,752,684); compositions in which a low reactivity magnesia is reacted with an acid aluminum phosphate complex containing an anion of a mineral acid (other than an oxyphosphorus acid) or of a carboxylic acid (U.S. Pat. No. 3,923,534); and compositions formed of a solution of an acid and aluminum phosphate (e.g., Al(PO.sub.4).sub.3) slurried with silica, alumina and magnesia (U.S. Pat. No. 3,991,254). The insulating materials of U.S. Pat. No. 3,752,684 require the removal of large amounts of water at elevated temperatures; the cold setting refractory materials of U.S. Pat. No. 3,923,534 require extended periods (e.g., 6-8 hours) to set and the slurries used to form the insulating structures of U.S. Pat. No. 3,991,254 must be fired at 500.degree. C. or above. Finally, mono-ammonium and diammonium phosphates have been reacted with dead-burned magnesium oxide. These compositions have a number of inherent disadvantages, among which are intense ammonia odor, and the formation on top of the resulting cements of a phosphate solution residue. Generally, such prior art inorganic resin systems using phosphates and magnesia have been of a character which has limited their uses to such applications as refractory linings, thermal insulation and use in preparing fast-setting, bonded aggregate structures as replacements for cements and mortars.